as fast as possible while being thorough and careful
Proceed with all deliberate speed.
The court said the changes should be made with all deliberate speed.
A question like the present should be disposed of without undue delay. But a State cannot be expected to move with the celerity of a private business man; it is enough if it proceeds, in the language of the English Chancery, with all deliberate speed.
Supreme Court Justice Oliver Wendell Holmes -- Virginia v. West Virginia, 222 U.S. 19–20 (1911)
While giving weight to these public and private considerations, the courts will require that the defendants make a prompt and reasonable start toward full compliance with our May 17, 1954, ruling. Once such a start has been made, the courts may find that additional time is necessary to carry out the ruling in an effective manner. ...take such proceedings and enter such orders and decrees consistent with this opinion as are necessary and proper to admit to public schools on a racially nondiscriminatory basis with all deliberate speed the parties to these cases.
Supreme Court Chief Justice Earl Warren -- Brown et al. v. Board of Education of Topeka, et al., 349 U.S. 301 (1954)